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OKAY!!! So i realized tha i was playing around with the anti surge ring this weekend and decided to seat it all the way and close up the MWE groove..... i didn’t notice any ill affects, only change really was the turbo whistle/whoosh quited down a little. But i never did a full WOT pull. I backed it out about .125 and now no more issues.

Naw. Not a fuel issue. Have it set up to where it starts at 60 and raises to about 80 with higher rpm. I have a nice bottom sump with mazed in baffle setup. 1/2” lines. And i had 3/4 tank of fuel. Definitely not a fuel issue though. As i would climb the grade to test it, i was literally coming up to 60psi then slowly trying to roll past it when it would drop and surge.

Only things I’ve touched since it was fine on the way home: removed and reinstalled the intermediate pipe and v band clamps. Supplied air pressure from 0-90psi a couple times up and down to the afc to make sure there were no leaks. Then hooked that back up. And moved the anti surge ring out .125”. Everything else was left the same.

How long do you think this modified HE351 would last at 900 hp?
Have you tested it for long?

The turbo/bearing never failed, but I did eventually crack the turbine housing so bad that it developed a couple external leaks. It was a well used slightly cracked housing to start with, I ported the wastegate passage to open up flow and it finally cracked so bad, it's almost unusable. I'd say I got 200+ quarter mile passes out of it and 100+ dyno runs in the 750 to 900 HP range.

One thing that really helped the HE351cw survive is I ran a fairly loose wastegate setup letting it fully open around 35 psi total boost pressure since this is where it ran the fastest quarter mile passes at the track. On the dyno we were seeing a 75 HP power dip mid power band where the wastegate would open a little too early and neuter power for a bit till the RPM came up and the atmosphere charger came up to full speed. A couple of turns on the turbo tuner and we had a smooth power curve with no dip in the middle of the power band.

So after having a copilot watch the gauges while I was paying attention to the road, we saw that the drive pressure is shooting from 90psi to 120psi instantly and seemingly randomly right before the surge starts and all boost is lost. I did some more testing, and reading, and tuning, and testing. And I think I have figured it out. I am pretty certain that all this was caused by opening up the vane TOO MUCH. I believe that once the nozzle got below the pedestal that the turbine sits on, the exhaust gases were creating a pocket of turbulence. I have since actually tightened up the spring so that the vane cant open as far and having been able to recreate the issue, YET.

Just wanted to update on this. Been driving this thing everyday and doing at least 1 WOT pull each day. Ever since i tightened the spring to where the coils would bind before the Nozzle opened past the 45* chamfer on the pedestal, i have actually had lower overall drive pressure and haven’t been able to recreate the drive pressure spike to 120psi before everything surging and losing boost until i completely let off and let it calm down... so i guess that is definitely something to keep in mind when mechanically controlling these VGTs.